1. Field of the Invention
The present invention relates to a motor driving apparatus and an initial driving method for a three-phase motor.
2. Discussion of the Related Art
A phase of a motor excited to obtain the maximum torque is determined according to positions of a rotator. While the rotator rotates, the position of the rotator can be sensed on the basis of a counter electromotive force. Therefore, the phase for the maximum torque is selectively excited according to the sensed position of the rotator, thereby driving the motor.
However, when the motor is initially driven, it is impossible to sense the position of the rotator on the basis of the counter electromotive force, so a position sensor is used. If the phase is not suitably excited according to the positions of the rotator, the motor may fail to be initially driven, take a relatively long time to be driven, and wastefully consume electric power.
In a structure such as a compressor, having a driving environment unsuitable for mounting the position sensor, there have been used various other sensing methods to sense the position of the rotator. For example, the rotator may be forcibly aligned by exciting a stator, and therefore the motor may be driven from the aligned position of the rotator.
Further, there is a method for sensing the initial position of the rotator without the position sensor, which is disclosed in Korean Patent First Publication No. 2000-0024078.
In this method, an excitation phase current is measured a total of six times according to two-phase excitation, and a current difference between the excitation currents measured when the same phase is excited is calculated. At this time, the position of the rotator can be detected on the basis of the calculated current difference, wherein a resoluble angle is an electrical angle of just about 60 degrees.
Further, a difference value between the calculated current differences is calculated on the basis of the calculated difference value when the rotator is placed at a position where there is no current difference between the excitation phase currents, i.e., where there is the minimum magnetic resistance.
However, in this conventional method of measuring the initial position of the rotator, it is difficult to determine the initial position of the rotator in the case of an interior permanent magnet (IPM) type motor that has recently been mostly used in a household motor such as a compressor.
FIG. 1 is a graph showing the excitation phase current difference and the difference value with respect to a mechanical angle according to the positions of the rotator in an IPM type four-pole motor.
Referring to FIG. 1, with regard to points A and B of the mechanical angle, the excitation phase current difference has the same positive and negative signs. Thus, the sign determination of the current difference cannot guarantee the correct measurement for the initial position of the rotator in all kinds of motors. Further, as described above, the resoluble angle reaches about 60 degree, so that it is difficult to precisely measure the position of the rotator.